Fair Value of Financial Assets and Liabilities (Fair Value Measurements, Recurring and Nonrecurring) (Details) (USD $)	Sep. 30, 2012		Dec. 31, 2011
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	$ 1,117,000,000		$ 861,000,000	[1]
Fixed income [Abstract]
Mark-to-market subtotal			(800,000,000)	[2],[3]
Other investments	19,000,000
Deferred compensation	(101,000,000)		(73,000,000)
Total assets	10,939,000,000		9,268,000,000
Total liabilities	(1,030,000,000)		(311,000,000)
Total net assets	9,909,000,000		8,957,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	101,000,000		73,000,000
Fair value swap contract current liability			503,000,000
Mark-to-market derivative liabilities (current liabilities)	521,000,000		112,000,000
Mark-to-market derivative liabilities (noncurrent liabilities)	407,000,000		126,000,000
Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	319,000,000		562,000,000
Equity Securities [Abstract]
Equity securities	1,452,000,000		1,275,000,000
Commingled funds	1,906,000,000		1,822,000,000
Equity securities subtotal	3,358,000,000		3,097,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,100,000,000		1,047,000,000
Debt securities issued by states of the United States and political subdivisions of the states	355,000,000		541,000,000
Debt securities issued by foreign governments	84,000,000		16,000,000
Corporate debt securities	1,734,000,000		778,000,000
Federal agency mortgage-backed securities	31,000,000		357,000,000
Commercial mortgage-backed securities (non-agency)	47,000,000		83,000,000
Residential mortgage-backed securities (non-agency)	15,000,000		5,000,000
Mutual funds fixed income	9,000,000		47,000,000
Fixed income subtotal	3,375,000,000		2,874,000,000
Direct lending securities	70,000,000		13,000,000
Other debt obligations	16,000,000		18,000,000
Nuclear decommissioning trust fund investments subtotal	7,138,000,000	[4]	6,564,000,000	[4]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	2,000,000		(57,000,000)
Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	21,000,000		35,000,000
Commingled funds	20,000,000		30,000,000
Equity securities subtotal	41,000,000		65,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	93,000,000		80,000,000
Debt securities issued by states of the United States and political subdivisions of the states	58,000,000		65,000,000
Corporate debt securities	260,000,000		314,000,000
Federal agency mortgage-backed securities	60,000,000		121,000,000
Commercial mortgage-backed securities (non-agency)	6,000,000		10,000,000
Commingled funds fixed income	43,000,000		20,000,000
Fixed income subtotal	520,000,000		610,000,000
Direct lending securities	64,000,000		37,000,000
Other debt obligations	1,000,000		13,000,000
Pledged assets for Zion Station decommissioning subtotal	626,000,000	[5]	725,000,000	[5]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from pledged assets			9,000,000
Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	2,000,000		2,000,000
Fixed income [Abstract]
Mutual funds	69,000,000	[6],[7]	34,000,000	[6],[7]
Rabbi trust investments subtotal	71,000,000		36,000,000
Deferred compensation	(54,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	54,000,000
Supplemental executive retirement plan fair value	15,000,000
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	28,000,000		25,000,000
Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges			857,000,000
Other derivatives	5,532,000,000		1,777,000,000
Proprietary trading	4,841,000,000		288,000,000
Effect of netting and allocation of collateral received/(paid)	(8,530,000,000)	[8]	(1,855,000,000)	[8]
Mark-to-market subtotal	1,843,000,000	[9]	1,067,000,000	[8],[9]
Interest rate mark to market derivative assets	125,000,000		15,000,000
Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges			(13,000,000)
Other derivatives	(4,390,000,000)		(1,257,000,000)
Proprietary trading	(4,781,000,000)		(264,000,000)
Effect of netting and allocation of collateral received/(paid)	8,337,000,000	[8]	1,315,000,000	[8]
Mark-to-market subtotal	(834,000,000)	[3],[9]	(219,000,000)	[3]
Interest rate mark to market derivative assets	(95,000,000)		(19,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair value of energy swap contract current liability	17,000,000		9,000,000
Fair value of energy swap contract noncurrent liability	53,000,000		97,000,000
Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	1,117,000,000		861,000,000	[1]
Fixed income [Abstract]
Mark-to-market subtotal			0	[2],[3]
Other investments	2,000,000
Deferred compensation	0		0
Total assets	4,188,000,000		3,837,000,000
Total liabilities	(131,000,000)		(1,000,000)
Total net assets	4,057,000,000		3,836,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Collateral received from counterparties, net of collateral paid to counterparties	175,000,000
Fair Value Inputs Level 1 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	319,000,000		562,000,000
Equity Securities [Abstract]
Equity securities	1,452,000,000		1,275,000,000
Commingled funds	0		0
Equity securities subtotal	1,452,000,000		1,275,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,100,000,000		1,014,000,000
Debt securities issued by states of the United States and political subdivisions of the states	0		0
Debt securities issued by foreign governments	0		0
Corporate debt securities	0		0
Federal agency mortgage-backed securities	0		0
Commercial mortgage-backed securities (non-agency)	0		0
Residential mortgage-backed securities (non-agency)	0		0
Mutual funds fixed income	0		0
Fixed income subtotal	1,100,000,000		1,014,000,000
Direct lending securities	0		0
Other debt obligations	0		0
Nuclear decommissioning trust fund investments subtotal	2,871,000,000	[4]	2,851,000,000	[4]
Fair Value Inputs Level 1 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	21,000,000		35,000,000
Commingled funds	0		0
Equity securities subtotal	21,000,000		35,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	78,000,000		54,000,000
Debt securities issued by states of the United States and political subdivisions of the states	0		0
Corporate debt securities	0		0
Federal agency mortgage-backed securities	0		0
Commercial mortgage-backed securities (non-agency)	0		0
Commingled funds fixed income	0		0
Fixed income subtotal	78,000,000		54,000,000
Direct lending securities	0		0
Other debt obligations			0
Pledged assets for Zion Station decommissioning subtotal	99,000,000	[5]	89,000,000	[5]
Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	2,000,000		2,000,000
Fixed income [Abstract]
Mutual funds	69,000,000	[6],[7]	34,000,000	[6],[7]
Rabbi trust investments subtotal	71,000,000		36,000,000
Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges			0
Other derivatives	994,000,000		0
Proprietary trading	1,631,000,000		0
Effect of netting and allocation of collateral received/(paid)	(2,597,000,000)	[8]	0	[8]
Mark-to-market subtotal	28,000,000	[9]	0	[8],[9]
Interest rate mark to market derivative assets	0		0
Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges			0
Other derivatives	(1,225,000,000)		(1,000,000)
Proprietary trading	(1,678,000,000)		0
Effect of netting and allocation of collateral received/(paid)	2,772,000,000	[8]	0	[8]
Mark-to-market subtotal	(131,000,000)	[3],[9]	(1,000,000)	[3]
Interest rate mark to market derivative assets	0		0
Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0	[1]
Fixed income [Abstract]
Mark-to-market subtotal			0	[2],[3]
Other investments	0
Deferred compensation	(101,000,000)		(73,000,000)
Total assets	6,032,000,000		5,237,000,000
Total liabilities	(555,000,000)		(183,000,000)
Total net assets	5,477,000,000		5,054,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	101,000,000		73,000,000
Collateral received from counterparties, net of collateral paid to counterparties	(359,000,000)		532,000,000
Fair Value Inputs Level 2 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0
Equity Securities [Abstract]
Equity securities	0		0
Commingled funds	1,906,000,000		1,822,000,000
Equity securities subtotal	1,906,000,000		1,822,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0		33,000,000
Debt securities issued by states of the United States and political subdivisions of the states	355,000,000		541,000,000
Debt securities issued by foreign governments	84,000,000		16,000,000
Corporate debt securities	1,734,000,000		778,000,000
Federal agency mortgage-backed securities	31,000,000		357,000,000
Commercial mortgage-backed securities (non-agency)	47,000,000		83,000,000
Residential mortgage-backed securities (non-agency)	15,000,000		5,000,000
Mutual funds fixed income	9,000,000		47,000,000
Fixed income subtotal	2,275,000,000		1,860,000,000
Direct lending securities	0		0
Other debt obligations	16,000,000		18,000,000
Nuclear decommissioning trust fund investments subtotal	4,197,000,000	[4]	3,700,000,000	[4]
Fair Value Inputs Level 2 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	0		0
Commingled funds	20,000,000		30,000,000
Equity securities subtotal	20,000,000		30,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	15,000,000		26,000,000
Debt securities issued by states of the United States and political subdivisions of the states	58,000,000		65,000,000
Corporate debt securities	260,000,000		314,000,000
Federal agency mortgage-backed securities	60,000,000		121,000,000
Commercial mortgage-backed securities (non-agency)	6,000,000		10,000,000
Commingled funds fixed income	43,000,000		20,000,000
Fixed income subtotal	442,000,000		556,000,000
Direct lending securities	0		0
Other debt obligations	1,000,000		13,000,000
Pledged assets for Zion Station decommissioning subtotal	463,000,000	[5]	599,000,000	[5]
Fair Value Inputs Level 2 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income [Abstract]
Mutual funds	0	[6],[7]	0	[6],[7]
Rabbi trust investments subtotal	0		0
Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges			857,000,000
Other derivatives	3,872,000,000		1,653,000,000
Proprietary trading	3,070,000,000		240,000,000
Effect of netting and allocation of collateral received/(paid)	(5,695,000,000)	[8]	(1,827,000,000)	[8]
Mark-to-market subtotal	1,247,000,000	[9]	923,000,000	[8],[9]
Interest rate mark to market derivative assets	125,000,000		15,000,000
Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges			(13,000,000)
Other derivatives	(2,814,000,000)		(1,137,000,000)
Proprietary trading	(2,881,000,000)		(236,000,000)
Effect of netting and allocation of collateral received/(paid)	5,336,000,000	[8]	1,295,000,000	[8]
Mark-to-market subtotal	(359,000,000)	[3],[9]	(91,000,000)	[3]
Interest rate mark to market derivative assets	(95,000,000)		(19,000,000)
Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0	[1]
Fixed income [Abstract]
Other investments	17,000,000
Deferred compensation	0		0
Total assets	719,000,000		194,000,000
Total liabilities	(344,000,000)		(127,000,000)
Total net assets	375,000,000		67,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Collateral received from counterparties, net of collateral paid to counterparties	(9,000,000)		8,000,000
Fair Value Inputs Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0
Equity Securities [Abstract]
Equity securities	0		0
Commingled funds	0		0
Equity securities subtotal	0		0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0		0
Debt securities issued by states of the United States and political subdivisions of the states	0		0
Debt securities issued by foreign governments	0		0
Corporate debt securities	0		0
Federal agency mortgage-backed securities	0		0
Commercial mortgage-backed securities (non-agency)	0		0
Residential mortgage-backed securities (non-agency)	0		0
Mutual funds fixed income	0		0
Fixed income subtotal	0		0
Direct lending securities	70,000,000		13,000,000
Other debt obligations	0		0
Nuclear decommissioning trust fund investments subtotal	70,000,000	[4]	13,000,000	[4]
Fair Value Inputs Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	0		0
Commingled funds	0		0
Equity securities subtotal	0		0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0		0
Debt securities issued by states of the United States and political subdivisions of the states	0		0
Corporate debt securities	0		0
Federal agency mortgage-backed securities	0		0
Commercial mortgage-backed securities (non-agency)	0		0
Commingled funds fixed income	0		0
Fixed income subtotal	0		0
Direct lending securities	64,000,000		37,000,000
Other debt obligations			0
Pledged assets for Zion Station decommissioning subtotal	64,000,000	[5]	37,000,000	[5]
Fair Value Inputs Level 3 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income [Abstract]
Mutual funds	0	[6],[7]	0	[6],[7]
Rabbi trust investments subtotal	0		0
Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges			0
Other derivatives	666,000,000		124,000,000
Proprietary trading	140,000,000		48,000,000
Effect of netting and allocation of collateral received/(paid)	(238,000,000)	[8]	(28,000,000)	[8]
Mark-to-market subtotal	568,000,000	[9]	144,000,000	[8],[9]
Interest rate mark to market derivative assets	0		0
Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges			0
Other derivatives	(351,000,000)		(119,000,000)
Proprietary trading	(222,000,000)		(28,000,000)
Effect of netting and allocation of collateral received/(paid)	229,000,000	[8]	20,000,000	[8]
Mark-to-market subtotal	(344,000,000)	[3],[9]	(127,000,000)	[3]
Interest rate mark to market derivative assets	0		0
Exelon Generation Co L L C [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	518,000,000		466,000,000	[1]
Fixed income [Abstract]
Other investments	19,000,000
Deferred compensation	(27,000,000)		(18,000,000)
Total assets	10,621,000,000		9,520,000,000
Total liabilities	(886,000,000)		(150,000,000)
Total net assets	9,735,000,000		9,370,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	27,000,000		18,000,000
Mark-to-market derivative liabilities (current liabilities)	504,000,000		103,000,000
Mark-to-market derivative liabilities (noncurrent liabilities)	355,000,000		29,000,000
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	319,000,000		562,000,000
Equity Securities [Abstract]
Equity securities	1,452,000,000		1,275,000,000
Commingled funds	1,906,000,000		1,822,000,000
Equity securities subtotal	3,358,000,000		3,097,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,100,000,000		1,047,000,000
Debt securities issued by states of the United States and political subdivisions of the states	355,000,000		541,000,000
Debt securities issued by foreign governments	84,000,000		16,000,000
Corporate debt securities	1,734,000,000		778,000,000
Federal agency mortgage-backed securities	31,000,000		357,000,000
Commercial mortgage-backed securities (non-agency)	47,000,000		83,000,000
Residential mortgage-backed securities (non-agency)	15,000,000		5,000,000
Mutual funds fixed income	9,000,000		47,000,000
Fixed income subtotal	3,375,000,000		2,874,000,000
Direct lending securities	70,000,000		13,000,000
Other debt obligations	16,000,000		18,000,000
Nuclear decommissioning trust fund investments subtotal	7,138,000,000	[4]	6,564,000,000	[4]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	2,000,000		(57,000,000)
Exelon Generation Co L L C [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents			0
Equity Securities [Abstract]
Equity securities	21,000,000		35,000,000
Commingled funds	20,000,000		30,000,000
Equity securities subtotal	41,000,000		65,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	93,000,000		80,000,000
Debt securities issued by states of the United States and political subdivisions of the states	58,000,000		65,000,000
Corporate debt securities	260,000,000		314,000,000
Federal agency mortgage-backed securities	60,000,000		121,000,000
Commercial mortgage-backed securities (non-agency)	6,000,000		10,000,000
Commingled funds fixed income	43,000,000		20,000,000
Fixed income subtotal	520,000,000		610,000,000
Direct lending securities	64,000,000		37,000,000
Other debt obligations	1,000,000		13,000,000
Pledged assets for Zion Station decommissioning subtotal	626,000,000	[10]	725,000,000	[10]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	5,000,000		9,000,000
Exelon Generation Co L L C [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	1,000,000
Fixed income [Abstract]
Mutual funds	13,000,000	[11],[12]
Rabbi trust investments subtotal	14,000,000		4,000,000	[11],[12]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	8,000,000		7,000,000
Exelon Generation Co L L C [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges			1,551,000,000
Other derivatives	5,884,000,000		1,777,000,000
Proprietary trading	4,841,000,000		288,000,000
Effect of netting and allocation of collateral received/(paid)	(8,530,000,000)	[8]	(1,855,000,000)	[8]
Mark-to-market subtotal	2,195,000,000	[13]	1,761,000,000	[13]
Interest rate mark to market derivative assets	111,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair value swap contract current asset	352,000,000		503,000,000
Fair value swap contract noncurrent asset	0		191,000,000
Exelon Generation Co L L C [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges	0		(13,000,000)
Other derivatives	(4,320,000,000)		(1,151,000,000)
Proprietary trading	(4,781,000,000)		(264,000,000)
Effect of netting and allocation of collateral received/(paid)	8,337,000,000	[8]	1,315,000,000	[8]
Mark-to-market subtotal	(764,000,000)		(113,000,000)
Interest rate mark to market derivative assets	(95,000,000)		(19,000,000)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	518,000,000		466,000,000	[1]
Fixed income [Abstract]
Other investments	2,000,000
Deferred compensation	0		0
Total assets	3,532,000,000		3,410,000,000
Total liabilities	(131,000,000)		(1,000,000)
Total net assets	3,401,000,000		3,409,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	175,000,000
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	319,000,000		562,000,000
Equity Securities [Abstract]
Equity securities	1,452,000,000		1,275,000,000
Commingled funds	0		0
Equity securities subtotal	1,452,000,000		1,275,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,100,000,000		1,014,000,000
Debt securities issued by states of the United States and political subdivisions of the states	0		0
Debt securities issued by foreign governments			0
Corporate debt securities			0
Federal agency mortgage-backed securities			0
Commercial mortgage-backed securities (non-agency)			0
Residential mortgage-backed securities (non-agency)			0
Mutual funds fixed income			0
Fixed income subtotal	1,100,000,000		1,014,000,000
Direct lending securities			0
Other debt obligations			0
Nuclear decommissioning trust fund investments subtotal	2,871,000,000	[4]	2,851,000,000	[4]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents			0
Equity Securities [Abstract]
Equity securities	21,000,000		35,000,000
Commingled funds			0
Equity securities subtotal	21,000,000		35,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	78,000,000		54,000,000
Debt securities issued by states of the United States and political subdivisions of the states			0
Corporate debt securities			0
Federal agency mortgage-backed securities			0
Commercial mortgage-backed securities (non-agency)			0
Commingled funds fixed income			0
Fixed income subtotal	78,000,000		54,000,000
Direct lending securities			0
Other debt obligations			0
Pledged assets for Zion Station decommissioning subtotal	99,000,000	[10]	89,000,000	[10]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	1,000,000
Fixed income [Abstract]
Mutual funds	13,000,000	[11],[12]
Rabbi trust investments subtotal	14,000,000		4,000,000	[11],[12]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges			0
Other derivatives	994,000,000		0
Proprietary trading	1,631,000,000		0
Effect of netting and allocation of collateral received/(paid)	(2,597,000,000)	[8]	0	[8]
Mark-to-market subtotal	28,000,000	[13]	0	[13]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges	0		0
Other derivatives	(1,225,000,000)		(1,000,000)
Proprietary trading	(1,678,000,000)		0
Effect of netting and allocation of collateral received/(paid)	2,772,000,000	[8]	0	[8]
Mark-to-market subtotal	(131,000,000)		(1,000,000)
Interest rate mark to market derivative assets	0		0
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0	[1]
Fixed income [Abstract]
Deferred compensation	(27,000,000)		(18,000,000)
Total assets	6,018,000,000		5,222,000,000
Total liabilities	(481,000,000)		(128,000,000)
Total net assets	5,537,000,000		5,094,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	27,000,000		18,000,000
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	(359,000,000)		532,000,000
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0
Equity Securities [Abstract]
Equity securities	0		0
Commingled funds	1,906,000,000		1,822,000,000
Equity securities subtotal	1,906,000,000		1,822,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0		33,000,000
Debt securities issued by states of the United States and political subdivisions of the states	355,000,000		541,000,000
Debt securities issued by foreign governments	84,000,000		16,000,000
Corporate debt securities	1,734,000,000		778,000,000
Federal agency mortgage-backed securities	31,000,000		357,000,000
Commercial mortgage-backed securities (non-agency)	47,000,000		83,000,000
Residential mortgage-backed securities (non-agency)	15,000,000		5,000,000
Mutual funds fixed income	9,000,000		47,000,000
Fixed income subtotal	2,275,000,000		1,860,000,000
Direct lending securities			0
Other debt obligations	16,000,000		18,000,000
Nuclear decommissioning trust fund investments subtotal	4,197,000,000	[4]	3,700,000,000	[4]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents			0
Equity Securities [Abstract]
Equity securities			0
Commingled funds	20,000,000		30,000,000
Equity securities subtotal	20,000,000		30,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	15,000,000		26,000,000
Debt securities issued by states of the United States and political subdivisions of the states	58,000,000		65,000,000
Corporate debt securities	260,000,000		314,000,000
Federal agency mortgage-backed securities	60,000,000		121,000,000
Commercial mortgage-backed securities (non-agency)	6,000,000		10,000,000
Commingled funds fixed income	43,000,000		20,000,000
Fixed income subtotal	442,000,000		556,000,000
Direct lending securities			0
Other debt obligations	1,000,000		13,000,000
Pledged assets for Zion Station decommissioning subtotal	463,000,000	[10]	599,000,000	[10]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal			0	[11],[12]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges			857,000,000
Other derivatives	3,872,000,000		1,653,000,000
Proprietary trading	3,070,000,000		240,000,000
Effect of netting and allocation of collateral received/(paid)	(5,695,000,000)	[8]	(1,827,000,000)	[8]
Mark-to-market subtotal	1,247,000,000	[13]	923,000,000	[13]
Interest rate mark to market derivative assets	111,000,000
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges	0		(13,000,000)
Other derivatives	(2,814,000,000)		(1,137,000,000)
Proprietary trading	(2,881,000,000)		(236,000,000)
Effect of netting and allocation of collateral received/(paid)	5,336,000,000	[8]	1,295,000,000	[8]
Mark-to-market subtotal	(359,000,000)		(91,000,000)
Interest rate mark to market derivative assets	(95,000,000)		(19,000,000)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0	[1]
Equity Securities [Abstract]
Equity securities	0
Fixed income [Abstract]
Other investments	17,000,000
Deferred compensation	0		0
Total assets	1,071,000,000		888,000,000
Total liabilities	(274,000,000)		(21,000,000)
Total net assets	797,000,000		867,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	(9,000,000)		8,000,000
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents			0
Equity Securities [Abstract]
Equity securities			0
Commingled funds	0		0
Equity securities subtotal	0		0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0		0
Debt securities issued by states of the United States and political subdivisions of the states	0		0
Debt securities issued by foreign governments			0
Corporate debt securities			0
Federal agency mortgage-backed securities			0
Commercial mortgage-backed securities (non-agency)			0
Residential mortgage-backed securities (non-agency)			0
Mutual funds fixed income			0
Fixed income subtotal	0		0
Direct lending securities	70,000,000		13,000,000
Other debt obligations			0
Nuclear decommissioning trust fund investments subtotal	70,000,000	[4]	13,000,000	[4]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents			0
Equity Securities [Abstract]
Equity securities			0
Commingled funds			0
Equity securities subtotal			0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies			0
Debt securities issued by states of the United States and political subdivisions of the states			0
Corporate debt securities			0
Federal agency mortgage-backed securities			0
Commercial mortgage-backed securities (non-agency)			0
Commingled funds fixed income			0
Fixed income subtotal			0
Direct lending securities	64,000,000		37,000,000
Other debt obligations			0
Pledged assets for Zion Station decommissioning subtotal	64,000,000	[10]	37,000,000	[10]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal			0	[11],[12]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges			694,000,000
Other derivatives	1,018,000,000		124,000,000
Proprietary trading	140,000,000		48,000,000
Effect of netting and allocation of collateral received/(paid)	(238,000,000)	[8]	(28,000,000)	[8]
Mark-to-market subtotal	920,000,000	[13]	838,000,000	[13]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges	0		0
Other derivatives	(281,000,000)		(13,000,000)
Proprietary trading	(222,000,000)		(28,000,000)
Effect of netting and allocation of collateral received/(paid)	229,000,000	[8]	20,000,000	[8]
Mark-to-market subtotal	(274,000,000)		(21,000,000)
Interest rate mark to market derivative assets	0		0
Commonwealth Edison Co [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		173,000,000	[1]
Fixed income [Abstract]
Deferred compensation	(9,000,000)		(8,000,000)
Total assets	9,000,000		194,000,000
Total liabilities	(431,000,000)		(808,000,000)
Total net assets	(422,000,000)		(614,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	9,000,000		8,000,000
Mark-to-market derivative liabilities (current liabilities)	17,000,000		9,000,000
Mark-to-market derivative liabilities (noncurrent liabilities)	53,000,000		97,000,000
Commonwealth Edison Co [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		2,000,000
Fixed income [Abstract]
Mutual funds	9,000,000		19,000,000
Rabbi trust investments subtotal	9,000,000		21,000,000
Commonwealth Edison Co [Member] | Derivative Financial Instruments Assets [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair value swap contract current asset	352,000,000		503,000,000
Fair value swap contract noncurrent asset	0		191,000,000
Commonwealth Edison Co [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	(422,000,000)	[2],[3]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair value of energy swap contract current liability	17,000,000		9,000,000
Fair value of energy swap contract noncurrent liability	53,000,000		97,000,000
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		173,000,000	[1]
Fixed income [Abstract]
Deferred compensation	0		0
Total assets	9,000,000		194,000,000
Total liabilities	0		0
Total net assets	9,000,000		194,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		2,000,000
Fixed income [Abstract]
Mutual funds	9,000,000		19,000,000
Rabbi trust investments subtotal	9,000,000		21,000,000
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	0	[2],[3]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0	[1]
Fixed income [Abstract]
Deferred compensation	(9,000,000)		(8,000,000)
Total assets	0		0
Total liabilities	(9,000,000)		(8,000,000)
Total net assets	(9,000,000)		(8,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	9,000,000		8,000,000
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income [Abstract]
Mutual funds	0		0
Rabbi trust investments subtotal	0		0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	0	[2],[3]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0	[1]
Fixed income [Abstract]
Deferred compensation	0		0
Total assets	0		0
Total liabilities	(422,000,000)		(800,000,000)
Total net assets	(422,000,000)		(800,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income [Abstract]
Mutual funds	0		0
Rabbi trust investments subtotal	0		0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	(422,000,000)	[2],[3]	(800,000,000)	[2],[3]
PECO Energy Co [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	528,000,000		175,000,000	[1]
Fixed income [Abstract]
Deferred compensation	(18,000,000)		(21,000,000)
Total assets	537,000,000		184,000,000
Total liabilities	(18,000,000)		(21,000,000)
Total net assets	519,000,000		163,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	18,000,000		21,000,000
PECO Energy Co [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	9,000,000	[14],[15]	9,000,000	[14],[15]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	14,000,000		13,000,000
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	528,000,000		175,000,000	[1]
Fixed income [Abstract]
Total assets	537,000,000		184,000,000
Total net assets	537,000,000		184,000,000
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	9,000,000	[14],[15]	9,000,000	[14],[15]
PECO Energy Co [Member] | Fair Value Inputs Level 2 [Member]
Fixed income [Abstract]
Deferred compensation	(18,000,000)		(21,000,000)
Total liabilities	(18,000,000)		(21,000,000)
Total net assets	(18,000,000)		(21,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	18,000,000		21,000,000
Baltimore Gas and Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	52,000,000		33,000,000
Fixed income [Abstract]
Deferred compensation	(5,000,000)
Total assets	57,000,000		33,000,000
Total liabilities	(5,000,000)
Total net assets	52,000,000		33,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	5,000,000
Baltimore Gas and Electric Company [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	5,000,000
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	52,000,000		33,000,000
Fixed income [Abstract]
Total assets	57,000,000		33,000,000
Total net assets	57,000,000		33,000,000
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	5,000,000
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 2 [Member]
Fixed income [Abstract]
Deferred compensation	(5,000,000)
Total liabilities	(5,000,000)
Total net assets	(5,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	$ 5,000,000

[1] Excludes certain cash equivalents considered to be held-to-maturity and not reported at fair value.

[2] The Level 3 balance includes the current and noncurrent liability of $352 million and $0 million at September 30, 2012, respectively, and $503 million and $191 million at December 31, 2011, respectively, related to the fair value of ComEd's financial swap contract with Generation which eliminates upon consolidation in Exelon's Consolidated Financial Statements.

[3] The Level 3 balance includes the current and noncurrent liability of $17 million and $53 million at September 30, 2012, respectively, and $9 million and $97 million at December 31, 2011, respectively, related to floating-to-fixed energy swap contracts with unaffiliated suppliers.

[4] Excludes net assets (liabilities) of $2 million and $(57) million at September 30, 2012 and December 31, 2011, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.

[5] Excludes net assets of $5 million and $9 million at September 30, 2012 and December 31, 2011, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.

[6] The mutual funds held by the Rabbi trusts include $54 million related to deferred compensation and $15 million related to Supplemental Executive Retirement Plan. These funds are classified as Level 1 as they are valued based upon quoted prices (unadjusted) in active markets.

[7] Excludes $28 million and $25 million of the cash surrender value of life insurance investments at September 30, 2012 and December 31, 2011, respectively.

[8] Includes collateral postings (received) from counterparties. Collateral (received) from counterparties, net of collateral paid to counterparties, totaled $175 million, $(359) million and $(9) million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of September 30, 2012. Collateral (received) from counterparties, net of collateral paid to counterparties, totaled $532 million and $8 million allocated to Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2011.

[9] The Level 3 balance does not include current and noncurrent assets for Generation and current and noncurrent liabilities for ComEd of $352 million and $0 million at September 30, 2012 and $503 million and $191 million at December 31, 2011, respectively, related to the fair value of Generation's financial swap contract with ComEd.

[10] Excludes net assets of $5 million and $9 million at September 30, 2012 December 31, 2011, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.

[11] The $13 million mutual funds held by the Rabbi trusts are classified as Level 1 as they are valued based upon quoted prices (unadjusted) in active markets.

[12] Excludes $8 million and $7 million of the cash surrender value of life insurance investments at September 30, 2012 and December 31, 2011, respectively.

[13] The Level 3 balance includes current and noncurrent assets for Generation of $352 million and $0 million at September 30, 2012 and $503 million and $191 million at December 31, 2011, respectively, related to the fair value of Generation's financial swap contract with ComEd, which eliminates upon consolidation in Exelon's Consolidated Financial Statements.

[14] The mutual funds held by the Rabbi trusts are classified as Level 1 as they are valued based upon quoted prices (unadjusted) in active markets.

[15] Excludes $14 million and $13 million of the cash surrender value of life insurance investments at September 30, 2012 and December 31, 2011, respectively.